There's a load of 55KW motor, which has ZENER soft starter attach to it. The facility has utility and generator power backup. The soft starter works fine on utility, but when it was powered by generator. It was told to me, the power side of the soft starter burnt up. Later on, it was repaired and works fine again on utility again. Generator is a new installation over there. They are afraid of running this again on the generator. I took some observations. The generator is 225KVA gas powered MAN(German brand). I observed the frequency fluctuates at constant load. It varies like 51.2HZ,53.0Hz, 52.3Hz, 51.2Hz. I also notice that much of the electronics of the generator were bypassed. I also took power factor measurement through a NOKIAN power factor panel. On utility I got 0.99PF, when generator was at no load 0.4PF, when on load 0.01-0.02PF. This power factor is very low. I don't know whether AVR of the generator is working or not.

Technician working their also told me about one thing more. They had two 30KW dryer on star/delta on another machine. One dryer start on star, at certain temperature it shift into delta[I didn't know why the tehnician said after attaining a temperature, I have seen shifting from star/delta on time basis, I confirmed again from him, did the motor convert into delta after attaining a specific time or temperature, he said temperature]. After 5 sec, another dryer of 30KW starts on start[when first motor keeps running on delta, the moment the another motor starts on star, the panel get's shutdown. The siemens PLC S7300 restarts, HMI restarts, motors shutdown. It indicates that maybe due to starting torque it might have causes the voltage to drop.This machine works fine on utility, every equipment of the facility works fine. So this is a clear indication, that there's something wrong with the generator. The generator cannot be change now. I need to do something to make their motors running.To install inverter on every drive that causes the problem, I don't know what to do. I don't have experience on Power Generator, it was told to me that you cannot take PF from the generator, unless the generator is at 40% of it's load. At no load, there's no flow of current, so you cannot take PF measurement. However, I have seen smaller pumps of the generator are running. Like Oil pump, water circulation pump of the generator. I don't want to turn the water pump, oil pump OFF! to take the reading, it's very risky and might cause the generator to suddenly seize and melts it's piston.I was also advised from somebody that maybe the generator one spark plug out of 12 is not working and maybe you are getting fluctuation because of 1 plug not working. Facility technician told me, this generator has been over hauled.This indicates that their are fewer chances of spark plugs to be faulty.Inverter and Soft starters are very expensive that can be installed, I'm afraid of giving them a go ahead,their would be no warranty if they get burnt up due to poor power supply from the generator. I would be solely responsible for any loss that happens. I have seen smaller inverters running on this generator below 10KW.Maybe smaller inverters can run, but not bigger inverters on poor PF. ABB inverters recommend around 0.98PF. I sent mail to ZENER australian soft starter company, but got no response of any kind. Some one said, maybe softstarter got burnt because the firing angle got out, because of changing frequency of the thyristor and because of this it got burnt. Smaller inverter is working, because I think there's no problem of misfiring of thyristor, because of AC->DC then DC->AC, inverter has complete control on frequency and no chance of misfiring because it's using DC as a source. As far as poor PF is concerned. I think maybe poor PF has enough current to give to the motors to get started and although they are very small, and inverters are very small size too. So there might not be heavy current demand. Please suggest what to do.

 

Is it a Question or Answer to any Question?

The Longest Question I have ever seen on this Website?

Good Questioning is also an ART?

Hope for you the best, If some one read it, understand it and reply you!!!!!!!!!!

 

From what I can ascertain from the first paragraph, it would seem that the 'standby' generator's prime mover governor is not working very well as it's not maintaining frequency. It's not clear if the frequency readings you provided were for loaded or unloaded operation, and what the load was if the readings were taken with load. But, in any case, the generator prime mover's governor is suspect.

Also, the AVR doesn't seem to be working very well.

So, it would seem that this new generator was not commissioned very well, and/or the operators are not operating it properly.

Most prime mover governors have two governor modes: Droop Speed Control and Isochronous Speed Control. Droop Speed Control governor mode is used when the generator and it's prime mover is operating in parallel with other generators and their prime movers, in other words, when connected to a grid. When isolated from a grid, the prime mover governor should be switched from Droop Speed Control governor mode to Isochronous Speed Control governor mode and that should cause the prime mover to very tightly control speed, which is directly proportional to frequency, in response to load changes. Or, if the prime mover governor does not have these two governor modes, then there must be some speed control regulator gain change to try to make the gen-set properly regulate frequency when disconnected from the grid and supplying the load.

AVRs also have different operating modes, and it's also possible that the operating mode is not being switched properly when disconnected from the grid. And, it may even be possible that the AVR isn't capable of responding to the changes in the reactive loading at your site.

Some soft starters can have large impacts on the power factor of small "island" power systems (power systems operating independently of large grids). A power system study may be required to determine if the generator's AVR can accommodate the reactive loads at your site.

I think you should try to get some basically resistive load of approximately 50% of generator rating (perhaps the dryers?) and at a stable load make sure the gen-set is properly controlling the frequency and the voltage and power factor. Then try to make a step change in load, resistive load as much as possible, and observe the gen-set's response. It should maintain frequency and voltage/power factor relative stably if working properly.

Once the gen-set is confirmed to be working properly, then you might want to try the soft-starter again. But, I would definitely recommend some engineering analysis of the soft-starter load and it's affect on the island system (generator, transformer(s), if any, and any load reactors which might be installed or might be necessary to "soften" the reactive load of the soft-starter).

I'm also curious because you said in the first paragraph that the generator was new, but in the second paragraph you said the generator was recently overhauled. And you talk about spark plugs for the generator's prime mover (the gas engine). I think a lot of us are very confused by all of the information and how it was presented.

But the indications all seem to be pointing to something wrong with the generator, it's prime mover governor, and possibly the AVR. Best to get them working as well as possible with resistive loads, or loads with light reactance (the dryers?) and then try the soft-starter again.

What does the soft-starter manual say about power supply fluctuations? What is the range of input frequency fluctuations it can accommodate?

Sometimes an email goes unanswered for some time; a phone call, if possible, is usually best. Or, if there's a manufacturer's representative in the area contact them for assistance.

 

Please Mr Umar i need your email. mine is mk_katep77[at]hotmail.com

 

umery2k75 at hotmail.com

 

The generator is from MAN. It's an old generator, it's basically a German brand. It was imported from a third party directly from Germany and then sold it to somebody else. I was baffled with the PF. So I managed to take readings of PF through a Nanovip Power Factor meter myself and on every point as I like.

I didn't get poor PF of the main generator, motors, machine incomers, etc. I got confused, because Power Factor panel was bypassed in generator mode and active on Utility power. So when I was taking reading through a Nokian Power Factor Controller I was getting wrong values, because no electricity was flowing through it, whereas their technician told me the PF is working on generator as well.

I took two types of readings in everywhere I can, one from utility and another from generator on the same load. Figures were 5% identical on nominal conditions, but dramatic change when motors starting from rest. I took readings on machines incomers, their individual motors, even recorded the peak current when motor starts from zero to star and then star to delta. I was then convinced that the AVR of the generator was working, because I was not getting Poor PF as before.

Although on load I have seen the generator working on 50Hz instead of 52Hz, because the guy who installed the generator, I had a telephonic conversation with him, he told me that he set this engine on 52Hz, because the cables were long 150meter from the generator to the load, so the voltage/current/frequency drops to 50Hz the point where it reaches the load. My GOD, the kind of people who are into business these days. The guy even told me he had taken training from U.K on generator. I then collected as many phone numbers of the generator peoples as I can on those days.

I called one person, he told me, they do this thing on old generators, because on load, the generator would come on 50Hz from 52Hz as on no load. So it's like a little margin they set. On No-load I have seen the generator running on 52Hz and on load it ran on 50Hz. So his statement was correct, but I'm still not convinced. I believe the electronic governor is not good. The generator functions were bypasses also, it was very badly operated.

I concluded the results as the generator can supply the power as we demand within the limit, but it has no derivate control. The problem that remains is to limit the inrush current of the motors that can affect the generator performance. One problem has been solved for the two 30KW motor dryer. I gave them a go ahead, because I got good PF readings from the generator. Their one unit is online now, also I have notice that people are the one that complicates the problem. A little over 1 week ago, they had changed their AVR of the generator, but nobody told me. They told me that their softstart got burnt and their dryer unit do not work. They complained of the voltage getting lower and other stuff.

So I bring my Power Analyzer equipment to check and record every situation. I was getting good result all the way and the machines starts on perfectly, then I asked you said the machine do not run. He added we didn't run after changing the AVR, we are telling you the symptoms we have observed before the AVR was changed.

I thought their readings were right. So this complicates the problem many times. Now the problem is with Soft Starter. I want to reduce the inrush current of it as much as I can. Tomorrow I'm going to reduce the acceleration time to maximum value and thinking of putting the motor on energy saving mode. Maybe this helps to reduce the inrush/nominal current.

Q1)Can I use a 3 phase choke on the input of the soft starter to reduce the inrush current?


I took these two readings on 30Kw motor. Please explain.

This motor starts from rest to star.This reading is accurate, I put the meter on capturing mode, to capture the values when the motor took the highest amp and what were the values of voltage and PF at that moment.

Q2)I don't understand why the PF becomes negative in this moment. This reading taken on utility.

OFF-STAR(Starting Peaking A)
Volt=400V
A=108
KW=49.9
PF=-0.67
Same reading taken on generator.
OFF-Star(Staring Peaking A)
Volt=8.15V
A=107
KW=1.31
PF=-0.87

"If I notice the current amperes almost same, but voltage drops alot on the motor terminal, when powered from generator and negative power factor almost similar, Please explain these two readings"

I have always seen motor converting from star->delta on a time basis, but on this dryer unit.It's the first time I have seen motors changing from star->delta after attaining a certain heating temperature of the machine,as set by the operator of the machine.

Q3)Have you people seen motors converting into delta on a temperature basis?

This reading was recorded, when it was running continuously.This reading taken on utility.
STAR(Running)
Volt=392V
A=20.1
KW=10.4
PF=0.79

I have asked a total of 3 questions, please specify. I would be thankful.

 

Umar,
You said:
<I called one person, he told me, they do this thing on old generators, because on load, the generator would come on 50Hz from 52Hz as on no load. So it's like a little margin they set. On No-load I have seen the generator running on 52Hz and on load it ran on 50Hz. So his statement was correct, but I'm still not convinced. I believe the electronic governor is not good. The generator functions were bypasses also, it was very badly operated.>

Check the heap of previous posts on the forum regarding droop - this is the effect you are seeing here. The relationship between speed and load in an isolated machine is linear so that as load increases the speed falls. If your speed changes from 52 Hz to 50 Hz as you go from no load to full load, this is a droop of 4% which is pretty well standard. Droop is not affected by cable length.

 

Umar Farooq... how about some basic data:

1) Engine - Hp, and Rpm?

2) Generator - kW, V, A, Rpm, and rated PF? Also its maximum kVAr output based on its excitation capability!

3) Utility Xfmr - kVA, V, A, and percent impedance?

4) Motor - kW, V, A, Rpm, and locked-rotor kVA to kW (or Hp) ratio?

5) Is your Power Analyzer capable of recording the basic AC parameters during acceleration from rest to normal speed?

Re ur Q1) No! The purpose of the soft-start controller is to eliminate high-inrush. Also, it should eliminate the Star-Delta starter!

Re ur Q2) There is no way starting-current can ever be "negative" meaning having leading PF!

Re ur Q3) You are listening to too many "experts!" Search Control List Archives for my definition!

Regards,
Phil Corso (cepsicon [at] aol [dot] com)

 

Thanks a lot for such useful insight and values. I didn't know much of them. It's a very good way, you summarize everything here. In a decent format and the factors which are to be taken into consideration.

If you would have not written this post. I would never come to know the systematic approach. I will go the other day over there to take these informations, not tommorow maybe, I will collect the pictures of it and also the values that you have listed.I will reconfirm the below values, these are all in my head now.

1)Engine is 225KVA,1500RPM(I will reconfirm RPM)

2)I need to study how generator produce KVar output and how much they can produce. I will also try to see if I get anything from the name plate of the generator regarding KVar.

3)I don't know about the utility transformer. I also didn't know, how I have to take into consideration the utility transformer. Good knowledge from you.

5)Yes, my power analyzer is capable of capturing the surge from rest to start. It's NANOVIP Power Factor instrument, made in United Kingdom.

Well..I have started the soft starter unit on the generator which was a success and also the two dryer 30KW two days back , the starter which had 55KW motor attach to it. What i did is that I reduce the acceleration to maximum that was 60sec instead of 4sec as previous. Also I put the stall protection, and did the hit and trial method. Just in case the motor stall, it would not exceed the current limitation during stalling and must be trip. I was disappointed as the current limit function wasn't able to start the motor properly and the motor was moving, but was not attaining a good speed. It was giving around 150Amps, where as Voltage Ramp was taking around 200+Amps. The motor was stalling again and again. I had to use the voltage ramp anyhow.

In the end I got the good setting, where the generator was able to pick that load up. The generator is not connected to any Power Factor improvement bank. The voltage that was on the outgoing terminal to motor was around 378Volts from soft starter, that I think is not good. It must be near to 400volts.

As far as I discuss the Negative Power Factor, I really don't know why I get the negative power factor. If even I get the negative PF, what does it mean? Is this bad? I asked my friend about this , but I discuss with him the application of star/delta. He said, the moment the star cuts and the delta connected, there's no flow of current. You get the highest amperes and negative PF. I then think, why would I get highest amp in that moment,even I get the negative PF. But I also observed the PF on soft starter, the negative power factor. In my industry, where I work there are many AC induction motors install from 0.5KW to 2MW. 2MW are not installed now, that plant is under commissioning, however I can get the values for 110,300Kw motors now. They are running and for smaller ones too.

 

to me it seems that there's no problem with all devices operating on utility, but the problem appears when the generator operates....
i suggests some questions for you to reply

1.is there automatic p.f.c for the device group operating on the emergency situation.

2.did you check the full load current for the devices

3. did you compare the full load current (operating on utility) with the calculated full load current of the generator.

what i want to tell that if you can determine the fault, you can call professionals to solve.

 

Umar,

A) What speed control your generator have ?, is it electronic ?, please send brand and model of speed control of the generator.

B) What Softstarter are you using, brand and model ? Some soft starter control two phases and the third phase pass thru, this softstart are not suitable
for use with electric generators like yours. They can work with the grid but not with electric generators.

C) Once you fix speed problems if they are present and the Generator is not in droop mode than we can start working on voltage
regulation problems, power factor, etc.

regards,